3131 results

  • The relationship between inundation duration and Spartina alterniflora growth along the Jiangsu coast, China

    Authors: Li, R.; Yu, Q.; Wang, Y.; Wang, Z.B.; Gao, S.; Flemming, B. (2018)
    Published in: Estuarine, coastal and shelf science (2018), page 1-32

    The above-ground biomass of Spartina alterniflora salt marsh meadows is influenced by numerous interacting factors, among them elevation, tidal range and inundation duration. Bio-geomorphological models make use of either linear or quadratic equations, but it is important to be aware that the variables are area specific and hence not generic. In order to explore the vegetation growth pattern and its influencing factors along the Jiangsu coast, China, field surveys were conducted in two typical S. alterniflora marshes along the coast of Dafeng and Rudong. To combine the influence of elevation and the effect of tidal range, the inundation ratio (IR) is introduced as a novel parameter, which is the ratio between inundation duration and the duration of the whole tidal period concerned. The relationship between above-ground biomass and IR can be expressed by a quadratic equation. The optimal inundation ratio for S. alterniflora along the Jiangsu coast ranges from 0.21 to 0.26, which is much lower than, for example, that for the marsh of North Inlet (0.35), South Carolina, and the Virginia Coast Reserve (0.41), USA. Tidal range plays a significant role in that a larger tidal range leads to a smaller optimal IR, and that the landward and seaward limits are displaced toward higher ground elevations. In macrotidal regions the submergence depth is larger, which results in enhanced submergence and salinity stress for the entire marsh, causing it to shift toward higher elevations. Tidal range is an important factor influencing the growth pattern of S. alterniflora, but geomorphological factors such as topographic profiles, and the presence of cliffs and tidal creeks must also be taken into account.

  • Morphodynamics of the Qiantang Estuary, China : controls of river flood events and tidal bores

    Authors: Xie, D.; Pan, C.; Gao, S.; Wang, Z.B. (2018)
    Published in: Marine geology (2018), page 1-23

    The importance of seasonal variations in river discharge on the morphological development of estuaries has been recognized in recent years, yet in situ observations about such variations are rare. Here we report a long-term dataset of bathymetry in the middle reach of the Qiantang Estuary, China, characterized by the presence of a large inner bar. Moreover, a hydrographic survey was carried out in the Yanguan reach where one of the largest tidal bores in the world occurs, covering a spring-neap tidal cycle in 2015. Meanwhile, detailed seasonal bathymetric data together with daily river discharges of 2015 were collected. The bed morphology shows strong seasonal and inter-annual variations. During the high flow season, the river flow erodes the bed and transports a large amount of sediments seaward. A good power-law relationship exists between the high river discharge and the channel volume at the upper estuary. Flood tides dominate under usual river flow condition. In particular, the tidal bore during spring and intermediate tides is characterized by large current velocity and high suspended sediment concentration, and transports a large amount of sediment landward. Over a year, a dynamic morphological equilibrium can be maintained. Moreover, the estuary has also been significantly influenced by the large-scale embankment in recent decades, constraining the lateral thalweg migration, bank erosion and point bar deposition, which usually occur in natural sinuous estuaries.

  • Designing a monitoring system to detect signals to adapt to uncertain climate change

    Authors: Haasnoot, M.; Klooster, S. van 't; Alphen, J. van (2018)
    Published in: Global environmental change : human and policy dimensions, volume 52 (2018), page 273-285

    Adaptive plans aim to anticipate uncertain future changes by combining low-regret short-term actions with longterm options to adapt, if necessary. Monitoring and timely detection of relevant changes, and critical transitions or tipping points is crucial to ensure successful and timely implementation and reassessment of the plan. Although efforts have been made to identify signposts to monitor, the question remains how to design a signal monitoring system that detects and anticipates (future) change to support adaptive planning. For example, to support water related infrastructure investments under uncertain climate change. What are good signposts to monitor and how to wisely analyse them to get timely and reliable signals for adaptation? In this paper, we present a framework for designing and using a monitoring plan as part of the Dynamic Adaptive Policy Pathways (DAPP) approach for decision making under uncertainty. We use the following criteria to evaluate signposts and their critical signal values: measurability, timeliness, reliability, convincibility and institutional connectivity. We illustrate the approach based on the signal monitoring system for the adaptive plan developed by the Delta Programme in the Netherlands.

  • Are water and conflict linked and what actually links them?

    Authors: Schmeier, S.; Baker, C.; Blaauw, E.M.; Iceland, C.; Meijer, K.S.; Sasse, R. (2018)

    The Water, Peace and Security partnership studies the pathways between water and conflict and the intervening factors. Based on this, it also advices relevant stakeholders to take appropriate action to prevent the deterioration of such situations. It does so by providing a comprehensive package of tools and knowledge that allow for global level analyses of potential water-related conflict hotspots and in-depth local analyses of those, for raising awareness among policy makers on required actions and for advice on which options are available to come to agreed action that can address both the natural and the socio-political aspects of the threat and thus ensure security, peace and sustainable development.

  • A multi-scale conceptual model of flood-tide delta morphodynamics in micro-tidal estuaries

    Authors: Austin, T.P.; Vila-Concejo, A.; Short, A.D.; Ranasinghe, R. (2018)
    Published in: Geosciences, volume 8 (2018) issue 9, page 1-20

    Wave and tide induced sediment transport pathways and rates govern the morphological evolution of estuarine systems. An understanding of the morphodynamics of these systems is required to maintain their commercial, biological and recreational value. The morphodynamics of Port Stephens estuary, a micro-tidal estuary located on a wave dominated southeast coast of Australia were investigated using bathymetric surveys and current velocity data from several locations over the estuary. This provided detailed insight into the rates and direction of movement for the main sedimentary features of the system, and how these features interact with the processes that drive their evolution. We used these findings to develop a conceptual model for estuarine morphodynamics that accounts for fair weather and storm conditions. Our model explains how sediment eroded from the estuarine beaches is trapped by the adjacent flood-tide delta. The model is applicable to fetch-limited estuaries that do not have offshore sources of sediment, where the tidal currents are weak in relation to the incident ocean waves, and that have a wide, stable entrance through which ocean waves can propagate into the estuary. The model is multi-scale in that it encapsulates both short-term and local process, and large scale evolution of an estuary; therefore, it represents a tool that may be used in developing sustainable estuary management strategies.

  • Joint assimilation of soil moisture retrieved from multiple passive microwave frequencies increases robustness of soil moisture state estimation

    Authors: Gevaert, A.I.; Renzullo, L.J.; Dijk, A.I.J.M. van; Woerd, H.J. van der; Weerts, A.H.; Jeu, R.A.M. de (2018)
    Published in: Hydrology and earth system sciences, volume 22 (2018), page 4605-4619

  • Plant functional diversity and nutrient availability can improve restoration of floating fens via facilitation, complementarity and selection effects

    Authors: Zuidam, J.P. van; Leeuwen, C.H.A. van; Bakker, E.S.; Verhoeven, J.T.A.; IJff, S.; Peeters, E.T.H.M.; Zuidam, B.G. van; Soons, M.B. (2018)
    Published in: Journal of applied ecology (2018), page 1-11

    Peat-forming wetlands, particularly floating fens that form the initial stages of these ecosystems, are declining globally due to excavation, dehydration and eutrophication. Restoration typically involves reestablishment of early-successional open-water stages, with oligotrophic conditions that are characteristic for these systems. However, restoration success is notoriously limited. A potential improvement may be to initiate succession by reintroducing of target plant species. Knowledge is therefore needed on (a) which plant functional groups should be reintroduced to stimulate fen formation; and (b) how to manage nutrient levels during restoration, considering that plant growth may be slow in oligotrophic conditions. We hypothesized that increasing functional diversity of introduced species would stimulate the formation of peat-forming target communities, their biomass accumulation and expansion onto open water. We also hypothesized that nutrient availability would mediate the relative contribution of specific functional groups to these effects. We investigated this in 36 artificial outdoor ponds by manipulating plant functional diversity (clonal dominants, clonal stress-tolerators and interstitials) on constructed rafts with fen-forming communities, and subjected these to a range of nutrient loadings over 2 years. Increasing functional diversity as well as increasing nutrient loadings had stimulating effects on plant biomass accumulation, cover formation and rhizome growth onto open water. Both complementarity (due to niche partitioning or facilitation) and selection effects were mechanisms underlying the diversity effect, with a constant relative importance over the entire range of nutrient availabilities. Different functional groups were important for biomass production at different nutrient availabilities. Rhizome formation by clonal stress-tolerators contributed disproportionately to open water colonization, identifying this functional group as key across all nutrient levels.

  • HIC 2018 : proceedings of the 13th International Conference of Hydroinformatics (Palermo, 1-6 July 2018)

  • Short-term control of a storage hydropower under flood risk by multi-stage stochastic optimization

    Authors: Uysal, G.; Sensoy, A.; Schwanenberg, D.; Alvarado Montero, R. (2018)
    Published in: HIC 2018 : proceedings of the 13th International Conference of Hydroinformatics (Palermo, 1-6 July 2018) (2018), page 1-7

    Operation of water structures especially with conflicting water supply and flood mitigation objectives is under more stress attributed to growing water demand and changing hydro-climatic conditions. Model Predictive Control (MPC) based optimal control solutions has been successfully applied to different water resources applications. In this study, Feedback Control (FBC) and MPC get combined and an improved joint optimization-simulation operating scheme is proposed. Water supply and flood control objectives are fulfilled by incorporating the long term water supply objectives into a time-dependent variable guide curve policy whereas the extreme floods are attenuated by means of short-term optimization based on MPC. A final experiment is carried out to assess the lead time performance and reliability of forecasts in a hindcasting experiment with imperfect, perturbed forecasts. The framework is tested in Yuvacık Dam reservoir where the main water supply reservoir of Kocaeli City in the northwestern part of Turkey (the Marmara region) and it requires a challenging gate operation due to restricted downstream flow conditions.

  • Conference on Big Data from Space (BiDS'17) : research, technology and innovation (28-30 November 2017, Toulouse, France)

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